Having sex with more than 10 partners over a lifetime can increase your chances of getting cancer, according to a shock new study.
And women with a higher number of sexual partners are more likely to report a limiting, long-term condition, experts from the UK, Austria, Turkey, Canada and Italy found.
The researchers analysed data from the English Longitudinal Study of Ageing (ELSA) involving adults aged 50 and over in England.
Some 5,722 participants reported how many sexual partners they had had and rated their health and any long-term condition on a questionnaire in 2012/13.
Those who had more sexual partners were younger, more likely to smoke, drink frequently, and do more vigorous physical activity each week, the researchers said.
The average age of participants was 64, and almost three-quarters were married.
Some 22% of men and and just under 8% of women reported 10 or more sexual partners.
The researchers found a statistically significant association between the number of lifetime sexual partners and risk of a cancer diagnosis among men and women.
Compared with women who reported 0-1 sexual partners, those who said they had had 10 or more had 91% increased odds of being diagnosed with cancer.
Men who reported 2-4 lifetime sexual partners were 57% more likely to have been diagnosed with cancer than were those who reported 0-1.
And those who reported 10 or more, were 69% more likely to have been diagnosed with the disease.
The study, published in BMJ Sexual & Reproductive Health, also found that women who reported five to nine, or more than 10 lifetime sexual partners were 64% more likely to have a limiting chronic condition than those who said they had had 0-1.
The researchers did not find any association in men.
While the study does not establish cause, it mirrors previous findings linking sexually transmitted infections in the development of several cancers and hepatitis.
The small number of cancer diagnoses in the participants meant the researchers were not able to analyse the results broken down by cancer type.
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If a causal relationship can be established in future, the authors suggest that asking people how many sexual partners they have had may help cancer screening programmes.
They write: "The finding that number of lifetime sexual partners is associated with limiting long-standing illness in women and not men should be noted.
"This gender difference is interesting, but an explanation is elusive, especially when men have a greater number of lifetime sexual partners than women, as shown in this study, and women are more likely to seek medical screening for STIs and are thus less likely to experience negative long-term health complications.
"Further research is required to identify mechanisms that explain this observed association and the divergent pattern between men and women."